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Unit notes and practice questions

Grade 9 Biology unit 6: Ecology

Everything here is for unit 6 of the Grade 9 Biology textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.

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Practice questions on unit 6

Short notes for unit 6

The cards filed under this chapter on the Grade 9 Biology page. Open one at a time.

InteractionSpecies 1Species 2Example
Competition−-−-Weeds and garden plants
Predation++−-Hawk eating a mouse
Herbivory++−-Caterpillar eating a leaf
Parasitism++−-Tick feeding on a host
Mutualism++++Acacia ants and acacia tree
Commensalism++00Cattle egrets and grazing cattle

When you use it

Use when identifying the outcome of species interactions on both organisms in an ecosystem.

Watch out

In competition, both interacting species experience a negative effect because a shared limiting resource is restricted.

Drafted from Grade 9 Biology, page 137 onwards, then checked twice before it went up

LevelDefinitionExample
OrganismIndividual living thingA single carp
PopulationSame species living in one areaAll carp in a lake
CommunityAll interacting populations in an areaFish, algae, and plants in a lake
EcosystemCommunity plus all abiotic factorsLiving community, water, and sunlight in a lake
BiosphereGlobal sum of all ecosystemsAll zones on Earth supporting life

When you use it

Use when ordering ecological units from a single organism up to the global biosphere.

Watch out

A community contains only the living populations, whereas an ecosystem includes both living and non-living abiotic factors.

Drafted from Grade 9 Biology, page 137 onwards, then checked twice before it went up

BiomeAnnual PrecipitationKey Physical FeatureDominant Vegetation
Tropical Rain Forest130 to 200 cmWarm year-round, high diversityBroad-leaf evergreen trees
DesertLess than 10 cmExtreme temperature variationSucculents such as cacti and euphorbs
Savanna30 to 50 cmLong dry season, seasonal firesGrasses and scattered fire-adapted trees
Boreal Forest (Taiga)40 to 100 cmLong cold winters, acidic soilConiferous trees like pine and spruce
Tundra20 to 60 cmPermafrost layer, short summerMosses, lichens, and dwarf shrubs

When you use it

Use when identifying terrestrial biomes by their precipitation range, climate characteristics, and plant types.

Watch out

Tundra has permanently frozen soil called permafrost, which prevents deep root growth and excludes large trees.

Drafted from Grade 9 Biology, page 137 onwards, then checked twice before it went up

FeaturePrimary SuccessionSecondary Succession
Starting substrateBare rock or lava with no soilPre-existing soil present
Pioneer speciesLichens and mossesGrasses and herbaceous plants
Starting causeVolcanic island or glacial retreatAbandoned farm, flood, or fire
Rate of recoveryHundreds to thousands of yearsMuch faster recovery

When you use it

Use when determining how an ecosystem colonizes barren land compared to recovering after an environmental disturbance.

Watch out

Secondary succession starts with pre-existing soil, meaning it does not require lichens to weather rock into soil.

Drafted from Grade 9 Biology, page 137 onwards, then checked twice before it went up

Practice questions on unit 6

10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.

Question 1

What is the scientific study of the relationships of organisms to one another and to their environment called?

  1. A.Natural history
  2. B.Ecology
  3. C.Geology
  4. D.Anatomy
Show the answer and why

Answer: B Ecology

Why

Ecology is the branch of biology that studies the relationships of living organisms to each other and to their surrounding environment.

Question 2

Which of the following is a living (biotic) component of an ecosystem?

  1. A.Soil pH
  2. B.Sunlight
  3. C.A predator
  4. D.Water
Show the answer and why

Answer: C A predator

Why

Biotic factors are the living components of an ecosystem, such as predators, herbivores, parasites, and competitors. Sunlight, water, and soil pH are abiotic (non-living) factors.

Question 3

What term describes a group of interbreeding organisms that belong to the same species and live in the same area at the same time?

  1. A.Population
  2. B.Biological community
  3. C.Ecosystem
  4. D.Biosphere
Show the answer and why

Answer: A Population

Why

A population is a group of interbreeding organisms of the same species living together in a specific area at the same time.

Question 4

In which type of ecological interaction do both interacting species receive benefits (+/+)?

  1. A.Parasitism
  2. B.Commensalism
  3. C.Mutualism
  4. D.Predation
Show the answer and why

Answer: C Mutualism

Why

Mutualism is an ecological relationship where individuals of both species benefit from the interaction.

Question 5

What is the typical salt concentration found in freshwater biomes such as streams, rivers, and lakes?

  1. A.Less than 1%
  2. B.Around 3%
  3. C.Around 10%
  4. D.More than 20%
Show the answer and why

Answer: A Less than 1%

Why

Freshwater biomes typically have salt concentrations of less than 1%, while marine biomes generally have salt concentrations around 3%.

Question 6

In the arctic tundra biome, what is the name of the permanently frozen layer of soil that restricts the growth of plant roots?

  1. A.Moraine
  2. B.Permafrost
  3. C.Topsoil
  4. D.Humus
Show the answer and why

Answer: B Permafrost

Why

Permafrost is the permanently frozen soil layer in the tundra that prevents deep root growth for trees and large plants.

Question 7

Which type of succession occurs when pioneer organisms begin colonizing a virtually lifeless area, such as a new volcanic island?

  1. A.Secondary succession
  2. B.Primary succession
  3. C.Deforestation
  4. D.Herbivory
Show the answer and why

Answer: B Primary succession

Why

Primary succession occurs when ecological colonization starts in a barren, virtually lifeless area with no pre-existing soil, such as new volcanic rock or moraine left by a glacier.

Question 8

Near Bishoftu, a student watches cattle egrets catching insects stirred up by grazing cattle. The birds get food, while the cattle are unaffected. What is this relationship called?

  1. A.Commensalism
  2. B.Herbivory
  3. C.Parasitism
  4. D.Competition
Show the answer and why

Answer: A Commensalism

Why

Commensalism is an interaction where one species benefits (+), while the other species is neither helped nor harmed (0).

Question 9

Temperature is a key abiotic factor affecting metabolism. Temperatures above what value destroy the enzymes of most living organisms?

  1. A.0 degrees Celsius
  2. B.25 degrees Celsius
  3. C.35 degrees Celsius
  4. D.45 degrees Celsius
Show the answer and why

Answer: D 45 degrees Celsius

Why

According to the textbook, temperatures above 45 degrees Celsius (113 degrees Fahrenheit) destroy the enzymes of most organisms.

Question 10

Which terrestrial biome covers about one-fifth of Earth's land, is located near 30 degrees north and south latitude, and receives less than 10 centimetres of rain per year?

  1. A.Savanna
  2. B.Desert
  3. C.Boreal forest
  4. D.Temperate broad-leaf forest
Show the answer and why

Answer: B Desert

Why

Deserts receive an average of less than 10 centimetres of rainfall annually, cover about one-fifth of Earth's land, and many are found at about 30 degrees north and south latitude.

The app holds 12 questions on this unit, marked as you go. These are the first 10.

The textbook pages for unit 6

The whole Grade 9 Biology textbook, free as a PDF.

Ministry of Education edition, English, 165 pages

Download the PDF

All Grade 9 Biology short notes

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